Pressure-sensitive adhesive (PSA) tapes are virtually ubiquitous in the home and workplace. In its simplest configuration, a pressure-sensitive tape comprises a PSA and a backing. The PSA is tacky at the intended use temperature, and adheres to a variety of substrates using only moderate pressure to form the bond. In this fashion, PSA tapes constitute a complete, self-contained bonding system.
According to the Pressure-Sensitive Tape Council, PSAs are known to possess properties including the following: (1) aggressive and permanent tack, (2) adherence with no more than finger pressure, (3) sufficient ability to hold onto an adherend, and (4) sufficient cohesive strength to be removed cleanly from the adherend. Materials that have been found to function well as PSAs include polymers designed and formulated to exhibit the requisite viscoelastic properties resulting in a desired balance of tack, peel adhesion, and shear holding power. PSAs are characterized by being normally tacky at room temperature (e.g., 20° C.). PSAs do not embrace compositions merely because they are sticky or adhere to a surface.
These requirements are assessed generally by means of tests which are designed to individually measure tack, adhesion (peel strength), and cohesion (shear holding power). These measurements taken together constitute the balance of properties often used to characterize a PSA.
With broadened use of PSA tapes over the years, performance requirements have become more demanding. Shear holding capability, for example, which originally was intended for applications supporting modest loads at room temperature, has now increased substantially for many applications in terms of operating temperature and load. So-called high performance pressure-sensitive tapes are those capable of supporting loads at elevated temperatures for 10,000 minutes. Increased shear holding capability has generally been accomplished by crosslinking the PSA, although considerable care must be exercised so that high levels of tack and adhesion are retained in order to retain the aforementioned balance of properties.
There are a wide variety of PSA materials available today, including natural crude or synthetic rubbers, block copolymers, and acrylic ester polymeric compositions. Acrylic ester PSAs in particular have been the focus of a great deal of development over the last half century as the performance demands for PSAs have increased. Acrylic ester PSAs may be closely tailored to provide a number of desired attributes such as, e.g., elasticity, tackiness, transparency, resistance to oxidation and sunlight, as well as have the necessary degree of adhesion and cohesion for demanding tape applications.
Poly(isobutylene), polyvinyl ethers, and polybutadiene can also be made into PSAs, but due to various deficiencies they are less common in the market.